1. Field of the Invention
Embodiments disclosed here generally relate to a downhole jarring tool. More specifically, embodiments disclosed herein generally relate to a downhole jarring tool configured to provide an increased impact.
2. Background Art
In the drilling of wells, a drill bit is used to dig many thousands of feet into the earth's crust. FIG. 1A shows one example of a conventional drilling system for drilling an earth formation. The drilling system includes a drilling rig 100 used to turn a drilling tool assembly which extends downward into a wellbore 102. The drilling tool assembly includes a bottomhole assembly (BHA) 106 disposed on a lower portion of a drill string 104. Looking to FIG. 1B, BHA 106 may include a drill bit 208, a bit sub 210, stabilizers 216, a drill collar 218, and a jarring tool 220. The BHA may also include measurement-while-drilling and/or logging-while-drilling equipment 212, a mud motor 214, and a jar impact amplifier or a jar accelerator 222.
During a drilling operation, one or more of the drilling tool assembly components may become stuck in the wellbore 102. The jarring tool 220 may be used to apply an impact load to the stuck component so that the stuck component may be dislodged and drilling operations may continue. Actuating jarring tool 220 to apply an upward jar includes applying a tensile force to drill string 104. Drill string 104 is held in place by the stuck component of the drilling tool assembly and the applied tensile force stretches drill string 104. As a result, energy is stored in drill string 104 in the form of material strain. Release of the applied tensile force transmits the energy stored in the stretched drill string 104 to the stuck component, thereby loosening the stuck component.
Looking to FIG. 2, a cross-sectional view of an example of a jarring tool 220 known in the prior art is shown. Jarring tool 220 includes an inner tubular 302 configured to connect with a drill string (not shown) and an outer tubular 304 configured to connect to a stuck object (not shown). Outer tubular 304 has an inner diameter 306 and a restriction 308 having a reduced inner diameter. A cavity 312 formed between inner tubular 302 and outer tubular 304 is filled with incompressible hydraulic fluid. As the drill string, and thus the inner tubular 302, are pulled upward, a sleeve assembly 310 disposed on inner tubular 302 and having an outer diameter approximately equal to the inner diameter of restriction 308 enters restriction 308. Movement of the incompressible hydraulic fluid around sleeve assembly 310 is thereby limited which provides for a build up of fluid pressure inside cavity 312. When sleeve assembly 310 exits restriction 308 as the drill string is moved upward into an upper portion of cavity 312 having inner diameter 306, high pressure fluid passes over sleeve assembly 310, thereby relieving the pressure differential and releasing energy stored by the high pressure fluid. The released energy accelerates sleeve assembly 310 and inner tubular 302 upward until two opposing shoulders 314, 316 disposed on inner and outer tubulars 302, 304, respectively, collide and provide an upward impact force which may dislodge the stuck object.
Alternatively, jarring tool 220 may be used to provide a downward jar by applying a compressive force to the drill string and inner tubular 302, thereby forcing sleeve assembly 310 downward through restriction 308. Fluid pressure build up occurs in a lower portion of cavity 312 and, when sleeve assembly 310 exits through a lower end of restriction 308, fluid pressure is relieved which releases stored energy, such that sleeve assembly 310 and inner tubular 302 are accelerated downward with respect to outer tubular 304. Two opposing shoulders 318, 320 disposed on inner and outer tubulars 302, 304, respectively, collide and provide a downward impact force to the stuck object.
To increase the amount of impact applied to the stuck component, accelerator tools known in the art may be used in combination with jarring tools. Accelerator tools allow additional energy to be stored that may be released when the jarring tool is actuated. The additional energy may increase the impact force transmitted to the stuck component which may help to dislodge the stuck component.
Accordingly, there exists a continuing need for improved jarring tools.